This invention relates to synthetic linear polyester compositions containing phosphorus. More particularly, the invention relates to melt blends of synthetic linear polyesters with certain polyphosphates which impart flame retardant properties to said compositions.
As is well known, certain polyesters enjoy widespread commercial acceptance for the production of oriented shaped articles such as fibers and films. However, most polyesters, and poly(ethylene terephthalate) and poly(tetramethylene terephthalate) in particular are flammable, i.e., not only are deficient in their ability to resist ignition upon application of flame but are also deficient in their ability to self-extinguish. This flammability makes commercial polyesters unsuitable for the production of fibers and film to be employed in such end-uses as children's clothing and sleepwear, carpets, sheets, and draperies.
Although the prior art contains some examples of non-flammable polyester compositions, none have found commercial acceptance for oriented shaped articles. Unfortunately, efforts to provide non-flammable polyester compositions have been successful only at the expense of fiber properties, such as tenacity, elongation, initial modulus, resilience, resistance to pilling, and color. The term "non-flammable" as used herein means the ability of a composition or shaped article or product made therefrom to self-extinguish upon removal of the flame source, in air.
U.S. Pat. No. 3,829,405 describes inter alia phosphorus-containing polyester compositions having improved flame retardant properties wherein said compositions comprise melt blends of a synthetic linear polyester with up to about 25 weight percent of a poly(phosphonate-phosphate)copolymer having the following average general formula: ##STR1## wherein R.sub.1 is a monovalent radical having up to about 20 carbon atoms selected from the group consisting of alkoxy, aryloxy, hydroxy, haloalkoxy, haloaryloxy, hydroxyalkoxy, and hydroxyaryloxy; R.sub.2 is a monovalent radical having up to 20 carbon atoms and is independently selected from the group consisting of hydrogen, alkyl, aryl, haloalkyl, and haloaryl; R.sub.3 is a monovalent radical having up to 20 carbon atoms and is selected from the group consisting of alkyl, aryl, haloalkyl, and haloaryl; Ar.sub.1 and Ar.sub.2 are divalent radicals each having up to about 20 carbon atoms independently selected from the group consisting of arylene and haloarylene; Z.sub.1 is a divalent radical selected from the group consisting of alkylene, arylene, haloalkylene, haloarylene, oxy, thio, and sulfonyl; Z.sub.2 is either hydrogen or ##STR2## m, n, and p are integers which independently are either 0 or 1 and at least one of m and p is 1; q and r are integers of at least 1; x is greater than one.